This invention relates generally to structural composites and, more particularly, to structural composites formed by a fiber reinforced resinous material which is chemically fused or bonded to the exposed edge, top and bottom surfaces of a cellular core material to provide a light weight monolithic composite of exceptionally high strength and load-bearing properties. The invention also relates to the process for preparing such composites.
Fiber reinforced composites are well known materials which are suitable for use in many industrial and structural applications. Generally speaking such composites are quite strong in relation to their weight and are formed by curing a resinous matrix material which has been impregnated into a mat, layer or other mass of reinforcing fibers. In addition to the reinforcing fibers and resin matrix, composites often include non-fiber reinforcing agents and/or core materials such as wood veneers, plastic chips, metal foil, cellular and non-cellular beads or the like as a means for tailoring the physical properties of the resulting composites. In such composites, the non-fiber reinforcing and/or core material generally are embedded or encapsulated in or otherwise surrounded by the fiber reinforced resinous matrix material.
There is a variety of resinous matrix materials, as well as reinforcing fiber and non-fibrous reinforcing and core materials, which have been used in the presentation of fiber reinforced composites, the selection of the various possible materials generally being dictated by the desired end use of a given composite.
Typically, glass, carbon, boron, metal or polymeric fibers, such as polyester or polyamide (nylon) fibers, are used as the reinforcing fibers. The fibers may be used, for example, in the form of rovings, mats, batts, woven and non-woven webs, or the like.
The resins which are used as the matrix materials normally comprise various heat hardenable epoxies, phenolics, nylons, polyesters, polyurethanes and polysulfides. The materials are well known and are readily available in commerce.
Typical non-fibrous reinforcing or core materials include hardwood or softwood veneers and blocks, metal foils, cellular and non-cellular polymeric beads, cellular and non-cellular polymeric particles or chips, metallic or polymeric honeycomb structures or the like. A particularly useful core material for preparing composites characterized by exceptionally light weight and high strength is balsa wood especially end-grain balsa wood, since it is dimensionally stable and has a cell structure which affords a combination of high rigidity and compressive and tensile strength that is superior to other materials of comparable density.
End-grain balsa-core structural materials are widely used in transportation and handling equipment, such as for floors of railroad cars, shipping containers, cargo pallets, bulkheads, doors and reefer bodies, as well as in a variety of other applications. These materials are also employed for structural insulation in aircraft applications, in housing and in boating. Balsa-core structural materials and methods for their preparation are described, for example, in U.S. Pat. Nos. 3,298,892 to Lippay, 3,325,037 to Kohn et al., 4,271,649 to Belanger, and 4,343,846, the disclosures of which are incorporated herein by reference.
Other patents which relate to fiber reinforced structural laminates and/or composites include U.S. Pat. Nos. 3,616,111 and 4,533,589. The disclosures of these patents are also incorporated herein by reference.